Norwich Crown Court heard that as the shopworker tried to open the till, Hackett, who was armed with a claw hammer, became impatient and banged the till with the weapon, breaking the till.

He then turned on the shopworker, punching him five times to the head and hitting him with the rounded end of the hammer to the side of the head.

Hackett then fled from the scene, grabbing just four packets of cigarettes worth £20.10.

Deborah Steele, prosecuting, said that the victim suffered a lump to the side of the head and had to be treated by ambulance staff who attended the scene.

Police said after the sentencing that forensic evidence and CCTV from the shop led officers to Hackett.

Investigating officer, Det Con Keith Linstead from Norwich CID, said: “This was a very serious offence committed by Hackett and one which was very frightening for his victims.

“The fact that he pleaded guilty at the earliest opportunity demonstrates how strong the case was against him. The four-year prison sentence reflects the serious nature of this offence and shows this type of crime will not be tolerated.”

The court heard that Hackett, of no fixed address, had a bad record, which included a previous conviction for robbery in Eastbourne in 2002.

Hackett appeared for yesterday’s court appearance via video link from Norwich prison and admitted the robbery at the newsagents, which happened at about 9.20pm on February 13.

Jailing him, Recorder Guy Ayers said: “You punched him on five occasions and used the hammer to strike him to the head.

“It is of particular significance that you did not just take the hammer with you, but you used it as part of the robbery. It is my duty to protect people that run small shops from people like you.”

Philip Farr, for Hackett, said that when he carried out the robbery he had been under the influence of drink and drugs, which had made him act in such an agitated state.

He said that Hackett was realistic about his sentence and asked that he be given full credit for his early guilty plea.

Mr Farr said that Hackett was planning to put his time in jail to good use to overcome his drink and drug problems.

Following the robbery, the victim told the The Evening News that he managed to grapple the weapon off his assailant and chase him out of the store.

The victim, who asked not to be identified, said the man had come into the shop and asked for the owner and for the best deal for beer. The man then became agitated, walking backwards and forwards, before punching the owner of the shop.

The worker said: “The guy then pushed him and said: ‘Why are you looking at me?’ Then he came this side of the counter and took a big hammer and asked: ‘Where’s the money? Give me money’.